|A boring grid.|
How was this done? Three ways: the use of the grid as a spatial organizer at the neighborhood level, and secondly by the use of main streets to reference and reinforce the grid, linking it between neighborhoods; the third element--perfected in Philadelphia's urban paradigm but seemingly lost outside of it--is the use of sub-grids, with their own internal spatial organization and reference-and-reinforcement networks, is connected with art of the grid in overarching city design, and seems a necessity to retain the grid's usefulness in terms of spatial organization without impairing it by overextension.
|Internal Spatial Organization in Wash West. Note mews.|
|The blue lines reference and reinforce the grid; the red lines break different grid alignments; the brown lines transect the grid without breaking it.|
How did this come to be? Reference and reinforcement. A reference is a main street a grid branches from; as the grid extends further from this street, another main street--a reinforcement--continues it. The part of West Philadelphia dominated by Lancaster Avenue is a perfect example of reference and reinforcement. Since Lancaster is the principal main street in the area, shouldn't it be a local grid reference? No...actually, the grid Lancaster exists in--and cuts across--references Powelton Avenue, and is later reinforced along 42nd St., thence Girard Avenue, and finally 63rd. Similarly, Southwest Philly's primary grid references Springfield Avenue first, and the Woodland Avenue (west of 49th), and is reinforced by Whitby and Elmwood Avenues.
The final element of reference and reinforcement is grid-breaking streets (or foils). These take two forms: either a street will transect an existing grid without getting referenced or reinforcing (such as Frankford, Ridge, Lancaster, or Passyunk), or it will divide different grid sections (such as Haverford, Baltimore, or Kensington). Both are necessary, as they interject variety into the otherwise monotonous grid.
Without reference and reinforcement, a grid will unravel itself. Market Street, once it becomes West Chester Pike, ceases to be referenced; the overarching grid unravels and becomes a series of highly localized mini-grids.
|Multiple grids in Philadelphia|
San Francisco is an exception to this rule, and in fact its main street (Market Street), functions as a foil, effecting the 45-degree split between the downtown and circumferential grids right in the middle of downtown. In addition, San Francisco's circumferential grid has some occasional kinks in it--a slight change of orientation following the reference and reinforcement streets, but no new references or reinforcements.
In Philadelphia, however, the situation is different. There is no circumferential grid, and only about half of the city is defined by the primary grid--referencing Market and Front, and reinforced primarily by Broad, 25th, and 30th. This grid looks like a north-south column with a long westerly branch. The rest of the city is defined by a succession of lesser grids: Southwest, referencing Springfield-49th-Woodland, and reinforced by Elmwood and Whitby; the River Wards, referencing Girard at first and then Richmond, and reinforced by Emerald; the Lower Northeast, referencing Cottman and reinforced by Devereux, Pratt, and Castor; and Powelton, referencing Powelton and reinforced by 42nd, Girard, and 63rd.
|Manayunk and Roxborough: looks like a grid, but really isn't.|
(Edit) I should talk about squares some. Squares are key public amenities that occur in any city building scheme. One of the great failures of the American grid is the failure to provide any. Even here, Victorian Philadelphia fails: the most important public squares, such as Rittenhouse or Franklin or Passyunk or Liberty Lands--and so on--either predate or postdate the Victorian era. Even today, carving out public squares in gentrifying neighborhoods is a strenuous issue. As such, every grid, to succeed, also has to have an internal method of providing public squares. The Billy Penn grid was one-off; Savannah's grid actually works best in this regard.
In sum, however, there are urban design principles in play in grids which do allow them, when those techniques are used properly, to grow organically and create a satisfying sense of place. Secondly, when the techniques are not present but an urban place where it looks like they ought to be is, this place is grid-like and in all likelihood evolved organically in the same way Koln's city center evolved organically out of the Roman grid of Colonia.
* Scientistic urban planning was led, in large part, by Lewis Mumford, who, like Carmello Sitte, idealized medieval urban design. Mumford was clearly influenced by Sitte (do read The Culture of Cities), which makes it kind of odd (and ironic) that other Modernist urban planners--especially those working under the Radiant City frame of reference--who would not so easily dismiss Mumford dismissed Sitte based on no more than some poor translation choices.